A power amplifier that is used in a base station that performs wireless communication is required to have a small size and high efficiency in consideration of cost. Further, high speed and broadband communication is progressing in the wireless communication field such as mobile phones and a broadband and high efficiency power amplifier is required for a base station. Envelop elimination and restoration (EER), which is one of the methods used for addressing the above demands, is disclosed in U.S. Pat. No. 6,256,482B1.
Further, in JP-A-2006-211112, a broadband D/A converter that uses an EER method and a broadband power amplifier using the same are disclosed. According to JP-A-2006-211112, the broadband D/A converter splits an input digital envelope signal for every frequency band, and n D/A converters individually convert digital envelope signals into analog signals. Furthermore, the converted analog signals are up-converted at predetermined frequency bands by individual up-converters and then added by an adder to be transmitted as an analog envelope signal corresponding to the original digital envelope signal.
In JP-A-2005-277559, a broadband and high efficiency EER transmitter is disclosed. According to the configuration of the transmitter disclosed in JP-A-2005-277559, an amplitude component of a modulation signal is input to a power supply terminal of a high-frequency power amplifier and a phase component thereof is input to a high frequency wave input terminal of the high-frequency power amplifier. Further, a modulated wave that is modulated from the original modulation signal is obtained through an output of the high-frequency power amplifier. An output of any of plural DC-DC converters is selected according to the level of the amplitude component as a power supply voltage of the transmitter.
In JP-A-Hei 11(1999)-127573, a parallel operating apparatus of a DC/DC converter is disclosed. The parallel operating apparatus of a DC/DC converter includes plural DC/DC converters that can be operated simultaneously and connected in parallel to each other, a current detecting circuit that detects the total current output from an output terminal, and a DC/DC converter on/off control circuit that controls the number of DC/DC converters to be operated according to the amount of total current.
In “High-Linearity RF Amplifier Design” (written by Peter B. Kenington, Artech house, 2000, PP 124-126), an example of s configuration of a class-S amplifier is disclosed. With this configuration, a PMW signal is generated by comparing an input waveform with a triangular wave, and the PMW signal is amplified by an amplifier including a pair of transistors in which a diode is inserted between a collector and an emitter. Further, a desired output is obtained by a low pass filter.